Still trying to "expand" my knowledge.. My thoughts today on both Air Entrainment and Steam your mileage may vary.
Air entrainment is not referring to pushing fire, but the simple fact that as a jet or stream of water is produced it displaces air in front of it, hence creating a lower pressure causing the higher pressure air around it to flow into the path. It is mechanical force acting on both products of combustion and products of extinguishment. Along with expansion & contraction of fire gases, which comes from gases both cooling and heating impacted by phase conversions of water and steam both condensation and evaporation.
It relatively easy to impact the flow of gases within a structure both by controlling vent path and by forcing it around via stream application. This is why many of us have argued for a water stream that produces the least amount of air entrainment along with the most contraction and cooling, while minimizing steam and expansion.
Solid or Straight handline streams can offer a high application rate and a low reaction force when configured correctly. This is the gold standard of critical flow.
Fog patterns on the other hand displace much more air. Air entrainment is massively increased over a jet of water resulting in displacement measured in cubic feet per minute. They also produce a finer droplet which easily converts to steam creating expansion and cooling surface fuels less effectively.
To close out my thoughts here are a fedw snippets from PhysLink.com:
Is the popular belief that 100C° (212F) steam is more injurious to the skin than boiling water (212F) just a wives tale?
Asked by: David